Harry Yeatman Internship
Stephanie F. Loria
08/31/09
Yeatman Internship: DNA Analysis of the Troglobitic Millipede Genus Tetracion
Research:
As part of the Yeatman internship, I analyzed the DNA of the millipede genus
Tetracion. Tetracion is a genus of troglobitic millipedes found in Tennessee and
Alabama (Shear 1969; Causey 1960; Hoffman 1956; Hoffman 1999; Shelley 1979;
Shelley 1996; Godwin). Two species have been described in this genus including
Tetracion jonesi and Tetracion tennesseensis. The ranges of T. jonesi and T.
tennesseensis are distinct with. T. jonesi inhabiting caves that are found primarily within
northeastern Alabama and some of southeastern Tennessee, while T. tennesseensis
inhabits caves that are in most of eastern Tennessee (The Nature Conservancy Survey
2005; Peck 1989; Causey 1960; Shear 1969; Shelley 1996; Hoffman 1999; Godwin).
Classification of species within Tetracion has been thus far, based solely on the
morphology of collected specimens. To better determine the relationship between the
two species of this genus, I decided to analyze their DNA. I sequenced the mitochondrial
gene cytochrome oxidase I from thirty-two T. tennesseensis individuals and thirteen T.
jonesi individuals. Based on preliminary analysis of the DNA of these individuals, I
found that the average percent genetic difference between individuals living in the same
cave was 0.19%. The average genetic difference for individuals within a species but
inhabiting different caves was 2.3% for T. tennesseensis and 1.1% for T. jonesi. The
percent genetic difference between the two species was somewhere between 7-10%.
Based on information about divergence rates cited by Thrope et al., I will suggest that
these two species probably split from each other between 3.5-5 million years ago.
However, further DNA analysis of these sequences will yield a more accurate estimate of
the time of this divergence. Also, more sequences need to be obtained from T. jonesi
individuals since only thirteen specimens have been successfully sequenced.
Evaluation of Yeatman Internship:
Because of the Yeatman Internship, I was able to focus on my research, which I
am not able to do most of the year due to other academic commitments. Therefore, I was
able to make great progress in my work. It was a good experience because I was fully
independent; I had to do every part of the process that is involved with this type of
research. I was to experience the daily life of full-time researcher.
References
Causey, N. B. Speciation in North American Cave Millipedes. 1960. The American
Midland Naturalist. 64: 116-122.
Godwin, J. The Biological Inventory of the Cave and Karst Systems of the Nature
Conservancy’s Sharp-Bingham Mountain Preserve. Alabama National Heritage
Program. 1-40.
Hoffman, R. L. Checklist of the Millipeds of North and Middle America. 1999. Virginia
Museum of Natural History.
Hoffman, R. L. New genera and species of cavernicolous diplopods from Alabama. 1956.
Alabama Geological Survey, Museum Paper. 35: 5-11.
Peck, S. B. The cave fauna of Alabama: Part I. The terrestrial invertebrates (excluding
insects) 1989. The NSS Bulletin. 11-33.
Shear, W. A. A synopsis of the cave milliped genera of the United States with an
illustrated key to genera. 1969. Pysche. 76: 123-146.
Shelley, R. 1996. The milliped order callipodida in western North America
Schizopetalidae: Tynommatinae). Entomolgical Scandanavia. 27: 25-64.
Shelley, R. A synopsis of the milliped genus Abacion Rafinesque (Callipodida,
Caspiopetalidae). 1984. Canadian Journal of Zoology. 62: 980-988.
The Nature Conservancy 2005. The Nature Conservancy. Tennessee Wildlife Refuge.
Thorpe, R. S., D. P. McGregor, A. M. Cumming, W. C. Jordan. DNA Evolution and
Colonization Sequences of Island Lizards in Relation to Geological History: mtdna rflp,
cytochrome B, Cytochrome Oxidase, 12s, RRNA Sequences, and Nuclear rapid Analysis.
1994. Evolution. 48: 230-240.